Method and arrangement for retransmission using HARQ

ABSTRACT

The present invention relates to a method and device for enhancing coverage of a power-limited mobile terminal by sending information relating to a single Hybrid Automatic Repeat Request (HARQ) process from the mobile terminal to a base station using several transmission time intervals.

TECHNICAL FIELD

The present invention relates to method and arrangement in a mobiletelecommunications network. In particular it relates to coverageenhancement for power-limited mobile terminals in the mobiletelecommunication network.

BACKGROUND

Mobile telecommunications network typically includes a radio accessnetwork connected to core network 100 as illustrated in FIG. 1. The corenetwork 100 can be interconnected with other networks and the radioaccess network comprises radio base stations 130 a-130 d, eachconfigured to communicate over the radio interface with mobile terminals150 located in the cell served by the respective radio base station.

At the cell-edge, the mobile terminals are sometimes power-limited, i.e.their transmission power is not sufficient to reach the targetedtransmission error rate, the so-called block error rate. It is thereforea need to find a solution for enhancing the coverage for power-limitedmobile terminals. HARQ (Hybrid Automatic Repeat reQuest) is a well-knowntechnique to mitigate such situations.

Automatic Repeat reQuest (ARQ) is an error control method for datatransmission which uses acknowledgments and timeouts to achieve reliabledata transmission. An acknowledgment is a message sent by the receiverto the transmitter to indicate that it has correctly received a dataframe or packet. A timeout is a reasonable point in time after thesender sends the frame/packet. If the sender does not receive anacknowledgment before the timeout, it usually re-transmits theframe/packet until it receives an acknowledgment or exceeds a predefinednumber of re-transmissions. A variation of ARQ is Hybrid ARQ (HARQ)which has better performance, particularly over wireless channels.

HARQ operation modes can use incremental redundancy and Chase combining.By using HARQ, the user data can be transmitted multiple times. For eachtransmission or retransmission either the same (Chase combining) orpotentially a different redundancy version (incremental redundancy) issent. When a corrupted packet is received, the receiver saves the softinformation, requests a retransmission by sending a negativeacknowledgement and later combines it with the already received softinformation with the soft information conveyed in the retransmissions torecover the error-free packet as efficiently as possible. By doing so itessentially accumulates the energy of all transmissions andretransmissions. Typically, after a few HARQ retransmissions the data issuccessfully received.

Consequently, a HARQ process takes care of the transmission of the firsttransmission and potential retransmissions at the sender side and thecorresponding reception at the receiver side. In addition, the senderside process interprets the HARQ feedback and the receiver sidegenerates the corresponding HARQ feedback according to the receptionstate

If the number of retransmissions that is required for a successfultransmission is growing, the retransmission delay is also increasingproportionally. For every retransmission round one HARQ Round Trip Time(RTT) is required. For some applications only a certain delay isacceptable. If such delay bounds need to be kept, alternative approachesare needed.

Another problem of the approach above is that the HARQ feedback istypically quite sensitive, since often only a single bit is used for ACKor NACK. Assuming that 9 retransmissions are needed and the HARQfeedback error rate is 10⁻³, this results in an overall probability thatat least one of the HARQ feedback is subject to a NACK-ACK error ofroughly 10⁻². Since such NACK-ACK error leads to a data packet loss,unless another retransmission protocol is used in addition to HARQ, alarge number of required HARQ retransmissions might lead to unacceptablepacket loss rates for certain applications. For example, 10⁻² is oftenmentioned as packet loss requirement for Voice over IP applications,i.e. less than 10⁻² IP packet should be lost to maintain an acceptablevoice quality.

One state-of-the-art approach to reduce the number of HARQretransmissions of a single HARQ process is segmentation at L2, which isillustrated in FIG. 2. In this solution user data is segmented insmaller portions that are then transmitted in independent HARQprocesses. I.e. each segment is subject for a HARQ feedback. Althoughthis solution reduces the risk of a HARQ feedback failure for a singleprocess, it does not reduce the probability of an IP packet loss, sinceall HARQ processes that carry a segment of the IP packet need to bereceived correctly. In total, the probability for a HARQ feedbackfailure is therefore in the same order.

Example: Instead of sending 264 bits of user data in one HARQ process,the user data might be split up in 4 parts leading to 4 HARQ processeswith 66 bits each. In the original case 16 HARQ transmissions might beneeded. For the L2 segmentation case, this would correspond to 4 HARQtransmissions for each process. These are in total still 16transmissions. However, they can be parallelized, since instate-of-the-art systems, several HARQ processes can be active at thesame time. Thus, the transmission delay can be reduced by L2segmentation.

However, the above described approach has the disadvantage that the L2protocol headers (e.g. MAC and RLC) that are needed to describe the userdata (e.g. Sequence Number, length) and the segmentation (segmentationflags, segment length in LTE) grows with increasing number of segments.In addition, typically L1 adds a checksum. Thus additional overhead isintroduced.

SUMMARY

The object of the present invention is to provide a solution forenhancing the coverage for power-limited terminals.

This is achieved by the present invention by using a plurality oftransmission time intervals for transmitting information relating to asingle HARQ process. I.e. information relating to one single HARQprocess is transmitted in a plurality of TTIs and no HARQ feedbackinformation is needed to trigger each of the transmissions. Theplurality of TTIs used for the transmissions relating to the single HARQprocess are considered as one resource which provides an increasedtransmission power compared to the case where only a single TTI is used.In order to avoid collisions with transmissions and retransmissionsreferred to as a first HARQ operation mode which uses a single TTI fortransmissions and retransmissions and where the timing relationshipbetween transmissions and retransmissions is pre-determined, theretransmissions of the present invention begin at least at a secondavailable retransmission occurrence according to the first HARQoperation mode. E.g. the retransmission may begin two or any integernumber of RTTs subsequent to the first TTI used for the transmission.The number of TTIs used for a transmission round may be configured byRRC signalling or by MAC scheduling grant.

According to a first aspect of the present invention, a method in amobile terminal wirelessly connectable to a radio base station of amobile telecommunication network is provided. The network supports atleast two HARQ operation modes of which the first HARQ operation modeuses a single TTI for transmissions and retransmissions and where thetiming relationship between transmissions and retransmissions ispre-determined and where the time between HARQ transmission andretransmission is defined as HARQ round trip time. It should also benoted that the time between one retransmission and a furtherretransmission also is a HARQ RTT. In the method information istransmitted according to the second HARQ operation mode relating to afirst HARQ process by using a first predetermined number of TTIscomprising at least a first TTI and a second TTI to the radio basestation. An indication that the transmitted information was not decodedcorrectly at the radio base station is received and the information isretransmitted according to the second HARQ operation mode relating tothe first HARQ process by using a second predetermined number of TTIs.The retransmission begins at least at a second available retransmissionoccurrence according to the first HARQ operation mode, subsequent to thefirst TTI.

According to a second aspect of the present invention, a method in theradio base station is provided. In the method, the mobile terminal isconfigured by the radio base station to transmit information, accordingto the second HARQ operation mode, relating to a first HARQ processusing a first predetermined number of TTIs comprising at least a firstTTI and a second TTI, to the radio base station, and to retransmit theinformation, according to the second HARQ operation mode, relating tothe first HARQ process using a second predetermined number of TTIs. Theretransmission begins at least at a second available retransmissionoccurrence according to the first HARQ operation mode, subsequent to thefirst TTI Information relating to the first HARQ process using the firstpredetermined number of TTIs comprising at least the first TTI and thesecond TTI is received, and HARQ feedback is transmitted in response tothe received information on the first determined number of TTIs.

According to a third aspect a mobile terminal wirelessly connectable toa radio base station of a mobile telecommunication network is provided.The mobile telecommunication network supports at least two HARQoperation modes of which the first HARQ operation mode uses a single TTIfor transmissions and retransmissions. For the first HARQ operationmode, the timing relationship between transmissions and retransmissionsis pre-determined the time between HARQ transmission and retransmissionis defined as HARQ round trip time. The mobile terminal comprises meansfor transmitting information according to the second HARQ operation moderelating to a first HARQ process by using a first predetermined numberof TTIs comprising at least a first TTI and a second TTI, to the radiobase station. It further comprises means for receiving an indicationthat the transmitted information was not decoded correctly at the radiobase station, and means for retransmitting the information according tothe second HARQ operation mode relating to the first HARQ process byusing a second predetermined number of TTIs. The retransmission beginsat least at a second available retransmission occurrence according tothe first HARQ operation mode, subsequent to the first TTI.

According to a fourth aspect of the present invention, a radio basestation of the mobile telecommunication network wirelessly connectableto a mobile terminal is provided. The mobile telecommunication networksupports at least two HARQ operation modes of which the first HARQoperation mode uses a single TTI for transmissions and retransmissions.For the first HARQ operation mode, the timing relationship betweentransmissions and retransmissions is pre-determined the time betweenHARQ transmission and retransmission is defined as HARQ round trip time.The radio base station comprises means for configuring the mobileterminal. The mobile terminal is configured to transmit information,according to the second HARQ operation mode, relating to a first HARQprocess using a first predetermined number of TTIs comprising at least afirst TTI and a second TTI, to the radio base station, and to retransmitthe information, according to the second HARQ operation mode, relatingto the first HARQ process using a second predetermined number of TTIs.The retransmission begins at least at a second available retransmissionoccurrence according to the first HARQ operation mode, subsequent to thefirst TTI, The radio base station further comprises means for receivinginformation relating to the first HARQ process using the firstpredetermined number of TTIs comprising at least the first TTI and thesecond TTI. Further, the radio base station comprises means fortransmitting HARQ feedback in response to the received information onthe first determined number of TTIs.

An advantage with embodiments of the present invention is that thesolution is efficient in terms of protocol header overhead, CRCoverhead, L1/L2 control signalling and HARQ feedback signalling.

Further advantages with embodiments of the present invention is that themechanism of the TTI bundling allows to artificially increase thetransmission time interval and thereby the coverage of power limitedterminals. Compared to prior art solutions the delay as well as thefailure probability is reduced. Furthermore, the solution is simple toincorporate with the state-of-the-art mode of operation.

The invention will now be described more in detail with the aid ofpreferred embodiments in connection with the enclosed drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically illustration of a mobile telecommunicationsnetwork wherein the present invention may be implemented.

FIG. 2 is an illustration of a message sequence chart for layer 2segmentation according to prior art.

FIG. 3 illustrates TTI bundling of 4 TTIs according to an embodiment ofthe present invention.

FIG. 4 also illustrates TTI bundling of 4 TTIs according to anembodiment of the present invention.

FIG. 5 illustrates another solution for enabling TTI bundling.

FIG. 6 illustrates a further solution for enabling TTI bundling.

FIGS. 7 a and 7 b, respectively shows a flowchart of the methodsaccording to one embodiment of the present invention.

FIG. 8 illustrates a mobile terminal and base station according to oneembodiment of the present invention.

DETAILED DESCRIPTION

Those skilled in the art will appreciate that the functions and meansexplained herein below may be implemented using software functioning inconjunction with a programmed microprocessor or general purposecomputer, and/or using an application specific integrated circuit(ASIC). It will also be appreciated that while the current invention isprimarily described in the form of methods and devices, the inventionmay also be embodied in a computer program product as well as a systemcomprising a computer processor and a memory coupled to the processor,wherein the memory is encoded with one or more programs that may performthe functions disclosed herein.

The present invention relates to the idea of using a plurality oftransmission time intervals (TTIs) to send information related to asingle HARQ process. This implies that an initial transmissionassociated with a HARQ process is followed by one or moreretransmissions associated with said HARQ process, wherein theretransmissions are sent independently of reception of any feedbackinformation. The initial transmission and the following retransmissionsrelating to the same HARQ process are sent without reception of anyfeedback information are referred to as a TTI bundle. The number of TTIor subframes used in a bundle is denoted as TTI bundle size. However,for one TTI bundle only one HARQ feedback signal is sent by thereceiver. This feedback is sent when all transmissions of a TTI bundleare received and processed. It should be noted that a TTI may also bereferred to as a subframe and the terms TTI and subframe areinterchangeable.

Essentially, the bundled TTIs are treated as a single resource.Therefore only a single scheduling grant or a single HARQ feedback isrequired to trigger transmissions or retransmissions, which results inthat the utilization of the corresponding signaling resources isreduced. The number of TTI:s used for the TTI bundle may be configuredby a MAC scheduling grant. Alternatively, the use of this method and/orthe configuration may be configured by an RRC signaling configurationmessage.

If the initial number of retransmissions is not sufficient for asuccessful reception, the receiver responds with a HARQ NACK. The HARQNACK or a specific scheduling grant triggers then one or more additionalHARQ retransmissions. This procedure continues until the HARQtransmission is completed successfully, i.e. that an ACK is received, orthat a criterion is reached, which determines that this HARQ processshould be terminated. For this example the HARQ process could beterminated when the maximum number of HARQ transmissions is reached.

According to a first embodiment of the present invention as illustratedin FIG. 3, a plurality of TTIs are bundled together implying that thesebundled TTIs 300 are used for an initial transmission relating to thesame HARQ process and subsequent bundled TTIs are used for subsequentHARQ retransmissions relating to the same HARQ process. A redundancyversion of the single HARQ process is sent in each TTI, without waitingfor any HARQ feedback information. Only when the information transmittedin the last TTI of the TTI bundle 300, 302 is received, HARQ feedback301, 303 is sent from the receiver of the information and expected bythe transmitter of the information. The timing when

HARQ feedback is expected to be sent is known at the data receiver. Alsowhen HARQ feedback is expected to be received is known at the datasender. If synchronous HARQ is used, special care has to be taken toalign the HARQ retransmissions into a HARQ process pattern. SynchronousHARQ is commonly understood as a HARQ operation where the retransmissionoccurs after a fixed and known time interval after the previoustransmission or retransmission. In contrast is an asynchronous HARQoperation, where this timing relation is not fixed and the scheduler hasa degree of freedom to decide when a retransmission is scheduled.Synchronous operation has the advantage that less control signalling isneeded, since the sender and receiver know when a retransmission is due.

The HARQ process pattern is illustrated in FIGS. 4-6. The HARQ feedbacksent in response to a TTI bundle is received too late for using thefirst TTI of the second HARQ RTT. Therefore, it is suggested to startthe HARQ retransmissions 406 synchronized with the normal HARQ MT, butwhere one HARQ RTT 404 remains idle, which is shown in FIG. 4. In FIG.4, the TTI bundle 407 consists of four TTIs, i.e. the TTIs denoted 1, 2,3, and 4. When the information in TTI4 is received, a feedback 409 issent to the transmitter. It should be noted that the transmission inTTI2, TTI3 and TTI4 is transmitted independently of an received HARQfeedback information. As explained above, this feedback 409 is receivedtoo late in order to start the retransmission in the first available TTI401 according to the normal operation mode, i.e. without TTI bundlingwhich also is referred to as the first operation mode. Thereforeadditional delay 405 is applied and the retransmission 406 starts atleast at the second available TTI 402, according to the first operationmode, in order to fit into the HARQ pattern of the normal operationmode. The first available TTI, or occurrence, for retransmissionaccording to the first HARQ operation mode is the first TTI which can beused for retransmission, e.g. the first TTI associated with the sameresource as the first TTI used for the initial transmission. Thisresults in that another mobile terminal with normal HARQ operation modecould use the resources in each occurrence of TTI 5 corresponding toHARQ process 5. This process does not collide in time with the fourprocesses used by the terminal applying TTI bundling according to thesecond operation mode. Without introducing the additional delay, acollision between transmissions of mobile terminals applying TTIbundling and those terminals that do not apply TTI bundling might occur.Thus collisions are efficiently avoided by introducing the additionaldelay. Another benefit of this approach is its simplicity and that itdoes not create any significant additional complexity for the scheduler.

As an example, assuming a HARQ RTT of eight TTIs in a typicalconfiguration four TTIs may be bundled as shown in FIG. 4. I.e. the TTIbundle size if 4 and four TTIs are treated as a single resource and usedfor transmission of information associated with a single HARQ process.This would give room for four bundled HARQ processes to be operated inparallel, two in each HARQ TTI. Even eight TTIs could be bundled, whichwould still allow two HARQ processes to be active at the same time.

A further possibility is to use the first possible TTI after the HARQfeedback has been received. This would correspond to the normalsynchronous HARQ operation. However, this approach has the disadvantagethat transmission collisions with other terminals might occur since theHARQ round trip time of this operation mode differs from the normal HARQRTT of users not using TTI bundles for their transmissions.

Moreover, only a small amount of extra signalling is required toconfigure TTI bundling according to the present invention. One typicaldeployment would be to configure cell-edge terminals to use for alltheir transmissions TTI bundling of some TTIs. Obviously, it isadvantageous to find a good match between the number of TTIs—this isequivalent to the number of HARQ processes used in normal HARQoperation—that spans one HARQ RTT and the number of TTIs used forbundling. For examples, assuming 8 TTIs for the HARQ RTT, a good choicewould be to allocate 2, 4, or 8 TTIs for one transmission bundle, sincethis allows using the remaining TTIs for other transmissions. Odd numberof TTIs would make this more difficult. For example if 3 TTIs would bebundled, this would also allow using 2 such processes in one HARQ MT,but two TTIs would be unused.

Turning now to FIGS. 7 a and 7 b illustrating flowcharts of the methodsto be implemented in a mobile terminal and in a base station,respectively. As illustrated in the flowchart of FIG. 7 a, a mobileterminal uses a plurality of transmission time intervals (TTIs) to sendinformation related to a single HARQ process to a base station.Initially in step 701, the mobile terminal receives information of atotal number of TTIs to be used for said transmission of informationrelating to the single HARQ process either by a MAC scheduling grant orby an RRC signalling configuration message sent 705 by the base station.This information may also comprise information that a plurality of TTIsshould be used for all its transmissions. Hence, in step 702, the mobileterminal transmits information relating to a first HARQ process using atleast a first and a second TTI, which implies that the TTI bundleconsists of two TTIs (bundle size=2), which is received 706 by the basestation. The information relating to the first HARQ process using atleast the second TTI is transmitted independently of any received HARQfeedback. In this case, two TTIs are bundled but it should be noted thatthe number of bundled TTIs are not limited to two or four as exemplifiedabove.

In accordance with the invention, the mobile terminal expects a singleHARQ feedback information associated with at least one of thetransmissions relating to the first HARQ process, e.g. associated withthe two transmissions relating to the first HARQ process. Compared tothe case where feedback is expected for each transmission, resources andtransmission power are saved. However, if each transmission would beresponded by HARQ feedback, it would be possible to ignore this feedbackat the data sender, since it knows that more up to date informationfollows.

If this transmission using the plurality of TTIs appears to beinsufficient for a successful decoding at the base station, the basestation responds 707 with a negative HARQ feedback, referred to as HARQNACK, which is received at the mobile terminal as shown in step 703.This HARQ NACK, or a specific scheduling grant, then triggers one ormore HARQ retransmissions transmitted 704 from the mobile terminal andreceived 708 at the base station. The retransmissions continues untilthe HARQ transmission is decoded successfully (i.e. when a positive HARQfeedback is received as illustrated in FIG. 7 a) or a criterion thatdetermines this HARQ process shall be terminated is reached.

Accordingly, in step 703, a negative HARQ feedback informationassociated with at least one of the transmissions relating to the firstHARQ process is received and in step 704 information relating to thefirst HARQ process, using at least one TTI is retransmitted in responseto the received negative HARQ feedback. In accordance with oneembodiment the same total number of TTIs denoted as TTI-bundle is usedfor the retransmission as for the transmission of information relatingto the first HARQ process. The retransmission starts at least at asecond available retransmission occurrence according to the first HARQoperation mode, subsequent to the first TTI as illustrated in FIG. 4.

A number of so-called slave processes may be bundled with the so-calledmaster process for the initial transmission attempt as illustrated inFIG. 5. In this case, an HARQ feedback is sent only for the masterprocess. A potential retransmission of the master process can then beperformed one MT after said master process. If the level of processbundling is determined by the scheduler in the base station the level ofprocess bundling must be signalled to the terminal. The information mayeither be provided dynamically via MAC control signalling or (semi-)statically via higher layer (RRC) control signalling.

The approach illustrated in FIG. 5 provides similar benefits as theabove described first embodiment. Four TTIs are used for an initialtransmission, where the first three TTIs are referred to as slaveprocesses and the transmission in the last TTI is the actual initialtransmission. The HARQ feedback is expected for the actual initialtransmission and one required retransmission is transmitted by using thefirst available TTI I.e. the TTI numbered 1 in FIG. 5 as the actualinitial transmission used TTI 1. An advantage is the shorter round triptime, i.e., the time between the last process of the initialtransmission attempt and the earliest possible retransmission. However,this approach may not allow bundling multiple processes for theretransmission(s) as the HARQ feedback is not yet available upon thesecond occurrence of processes 6, 7 and 8. This mobile terminal couldconsequently not achieve the theoretically achievable throughput as someprocesses remain unused in case of retransmissions. Note that in theexample provided in FIG. 5, two sets of processes can be scheduled (6,7, 8, 1 and 2, 3, 4 5).

In accordance with a further alternative, the actual round trip time aswell as the throughput are optimized by adapting the process numberingto the level of process bundling as illustrated in FIG. 6. The mainadvantage is that a terminal may use all TTIs for transmission whichensures high throughput. Also the MT is minimized even thoughpotentially slightly higher than with approach illustrated in FIG. 5.

However, the scheduler must handle the process identities separately permobile terminal. Possible differences between the actual HARQ RTTsincrease the risk for blocking, i.e., that a mobile terminal cannot bescheduled mobile terminal to a potentially upcoming retransmission ofanother mobile terminal.

The number of TTIs that are used in the first transmission round totransmit redundancy versions for a particular PDU is either signalled ina MAC control message denoted here as scheduling grant or is configuredfor that mobile terminal via RRC signaling. In the latter case thenumber of TTIs used for transmissions is typically valid for a longerperiod of time. However, it maybe reconfigured, if needed to increasethe radio resource efficiency. Obviously it is also possible to use apredetermined bundle size and to use MAC or RRC signalling forconfiguring the mobile terminal to use either the first or second HARQoperation mode.

Furthermore, the approach according to the embodiments of the inventionis flexible. The mobile terminals could be configured to use anarbitrary number of TTIs for their transmissions and retransmissions,where the number of TTIs used for the transmission and theretransmissions may differ. Hence, in principle, the number of TTIs usedfor HARQ retransmissions could be chosen independently from the numberof TTIs used for the first transmission. However, a simple approachwould be to use the same amount of TTIs for the transmission as theretransmissions, which would simplify the resource allocation for thescheduler and would give 3 dB gain for one HARQ retransmission.

In addition, TTI bundling can be applied for both dynamic andsemi-persistent scheduling. In both cases, the mobile terminal could beconfigured via RRC that TTI bundling should be used for all itstransmissions. If such configuration takes place via RRC, the normalL1/L2 grant format can be re-used. There is no need for a dedicatedgrant format.

The mechanisms of the embodiments of the present invention may be usedin combination with layer 2 (L2) segmentation. L2 segmentation implies,as stated above, that user data is segmented in smaller portions whereineach of the smaller portions then is transmitted in an independent HARQprocesses.

Furthermore, the present invention also relates to a mobile terminal 150wirelessly connectable to a radio base station 130 b of a mobiletelecommunication network. The mobile terminal 150 is illustrated inFIG. 8 and comprises means for transmitting 805 and receiving 806. Thetransmitter 805 is configured to transmit information 808 relating to afirst HARQ process using a first predetermined number of TTIs comprisingat least the first TTI and the second TTI. The receiver 806 isconfigured to receive feedback information 809 and may also beconfigured to receive 804 the configuration information 807 of the firstpredetermined number of TTIs either by RRC signalling or by MACsignalling and information via RRC signalling that a first predeterminednumber of TTIs comprising at least a first TTI and a second TTI shouldbe used for all its transmissions.

In addition, the transmitter 805 is configured to retransmit informationrelating to the first HARQ process, using a second predetermined numberof TTIs comprising at least one TTI, beginning at least at a secondavailable retransmission occurrence according to the first HARQoperation mode, subsequent to the first TTI. Similar to the firstpredetermined number of TTIs, also the second predetermined number ofTTIs may be received at the mobile terminal either by RRC signalling orby MAC signalling.

According to one embodiment, the first predetermined number of TTIs isequal to the second predetermined number of TTIs.

Moreover, the present invention concerns a radio base station 130 b of amobile telecommunication network wirelessly connectable to the mobileterminal 150 as illustrated in FIG. 8. The mobile telecommunicationnetwork supports at least two HARQ operation modes of which the firstHARQ operation mode uses a single TTI for transmissions andretransmissions. The first HARQ operation mode is also referred to asthe normal operation mode. The timing relationship in the first HARQoperation mode between transmissions and retransmissions ispre-determined and the time between HARQ transmission and retransmissionis defined as HARQ round trip time. The radio base station comprisesmeans for configuring 801 the mobile terminal 150 to transmitinformation 808, according to the second HARQ operation mode, relatingto a first HARQ process using a first predetermined number of TTIscomprising at least a first TTI and a second TTI, to the radio basestation, and to retransmit the information 808, according to the secondHARQ operation mode, relating to the first HARQ process using a secondpredetermined number of TTIs. The retransmission begins at least at asecond available retransmission occurrence according to the first HARQoperation mode, subsequent to the first TTI The radio base stationfurther comprises means for receiving 802 information relating to thefirst HARQ process using the first predetermined number of TTIscomprising at least the first TTI and the second TTI, and means fortransmitting HARQ feedback 809 in response to the received information808 on the first determined number of TTIs.

The embodiments of the present invention may be used in an LTE networkas illustrated in FIG. 1. Furthermore, the embodiments are applicablefor both the Time Division Duplex mode and the Frequency Division Duplexmode of LTE. It should however be noted that the present invention isnot limited to LTE but can be used in any communication network applyingsome kind of automatic repeat request functionality.

Accordingly, while the present invention has been described with respectto particular embodiments (including certain device arrangements andcertain orders of steps within various methods), those skilled in theart will recognize that the present invention is not limited to thespecific embodiments described and illustrated herein. Therefore, it isto be understood that this disclosure is only illustrative. Accordingly,it is intended that the invention be limited only by the scope of theclaims appended hereto.

1. A method in a mobile terminal wirelessly connectable to a radio basestation of a mobile telecommunication network that supports at least twoHybrid Automatic Repeat Request (HARQ) operation modes, of which thefirst HARQ operation mode uses a single Transmission Time Interval (TTI)for transmissions and retransmissions and where the timing relationshipbetween transmissions and retransmissions is pre-determined, said methodcomprising the steps of: transmitting information according to thesecond HARQ operation mode relating to a first HARQ process, by using afirst predetermined number of transmission time intervals (TTIs)comprising at least a first TTI and a second TTI, to the radio basestation, wherein a redundancy version of the first HARQ process is sentin each TTI; receiving an indication that the transmitted informationwas not decoded correctly at the radio base station; and retransmittingthe information according to the second HARQ operation mode relating tothe first HARQ process, by using a second predetermined number of TTIs,wherein the retransmission begins at least at a second availableretransmission occurrence according to the first HARQ operation mode,subsequent to the first TTI.
 2. The method of claim 1, wherein theretransmission begins at the second available retransmission occurrenceaccording to the first HARQ operation mode, subsequent to the first TTI.3. The method of claim 1, wherein the method comprises an initial stepof: receiving information indicating the first or second predeterminednumber of TTIs to be used for said transmission of information relatingto the first HARQ process.
 4. The method of claim 1, wherein the firstpredetermined number of TTI is equal to the second number of TTIs. 5.The method of claim 1, wherein the method further comprises the step of:receiving information via Radio Resource Control (RRC) signaling that afirst predetermined number of TTIs comprising at least a first TTI and asecond TTI should be used for all transmissions.
 6. The method of claim1, wherein the indication that the transmitted information was notdecoded correctly at the radio base station is an HARQ feedback.
 7. Amethod in a radio base station of a mobile telecommunication networkwirelessly connectable to a mobile terminal, the mobiletelecommunication network supports at least two Hybrid Automatic RepeatRequest (HARQ) operation modes of which the first HARQ operation modeuses a single Transmission Time Interval (TTI) for transmissions andretransmissions and where the timing relationship between transmissionsand retransmissions is pre-determined, said method comprising the stepsof: configuring the mobile terminal to transmit information, accordingto the second HARQ operation mode, relating to a first HARQ processusing a first predetermined number of transmission time intervals (TTIs)comprising at least a first TTI and a second TTI, to the radio basestation, wherein a redundancy version of the first HARQ process is sentin each TTI, and to retransmit the information, according to the secondHARQ operation mode, relating to the first HARQ process using a secondpredetermined number of TTIs, wherein the retransmission begins at leastat a second available retransmission occurrence according to the firstHARQ operation mode, subsequent to the first TTI; receiving informationrelating to the first HARQ process using the first predetermined numberof TTIs comprising at least the first TTI and the second TTI; andtransmitting HARQ feedback in response to the received information onthe first determined number of TTIs.
 8. The method of claim 7, whereinthe retransmission is configured to begin at the second availableretransmission occurrence according to the first HARQ operation mode,subsequent to the first TTI.
 9. The method of claim 7, wherein theconfiguring step further comprises: transmitting information indicatingthe first or second predetermined number of TTIs.
 10. The method ofclaim 9, wherein the first predetermined number of TTI is equal to thesecond number of TTIs.
 11. The method of claim 10, wherein theconfiguring step further comprises: transmitting information via RadioResource Control (RRC) signaling that a first predetermined number ofTTIs comprising at least a first TTI and a second TTI should be used forall transmissions.
 12. A mobile terminal wirelessly connectable to aradio base station of a mobile telecommunication network that supportsat least two Hybrid Automatic Repeat Request, HARQ, operation modes ofwhich the first HARQ operation mode uses a single Transmission TimeInterval (TTI) for transmissions and retransmissions and where thetiming relationship between transmissions and retransmissions ispre-determined, said mobile terminal comprising: a transmitter fortransmitting information according to the second HARQ operation moderelating to a first HARQ process by using a first predetermined numberof TTIs comprising at least a first TTI and a second TTI to the radiobase station, wherein a redundancy version of the first HARQ process issent in each TTI; and a receiver for receiving an indication that thetransmitted information was not decoded correctly at the radio basestation; wherein said transmitter is configured for retransmitting theinformation according to the second HARQ operation mode relating to thefirst HARQ process by using a second predetermined number of TTIs, andwherein the retransmission begins at least at a second availableretransmission occurrence according to the first HARQ operation mode,subsequent to the first TTI.
 13. The mobile terminal of claim 12,wherein the retransmission begins at the second available retransmissionoccurrence according to the first HARQ operation mode, subsequent to thefirst TTI.
 14. The mobile terminal of claim 12, wherein the mobileterminal is configured for receiving information indicating the first orsecond predetermined number of TTIs to be used for said transmission ofinformation relating to the first HARQ process.
 15. The mobile terminalof claim 12, wherein the first predetermined number of TTI is equal tothe second number of TTIs.
 16. The mobile terminal of claim 12, whereinthe indication that the transmitted information was not decodedcorrectly at the radio base station is an HARQ feedback.
 17. The mobileterminal of claim 12, wherein the mobile terminal is configured forreceiving information via Radio Resource Control (RRC) signaling that afirst predetermined number of TTIs comprising at least a first TTI and asecond TTI should be used for all its transmissions.
 18. A radio basestation of a mobile telecommunication network wirelessly connectable toa mobile terminal, the mobile telecommunication network supports atleast two Hybrid Automatic Repeat Request, HARQ, operation modes ofwhich the first HARQ operation mode uses a single Transmission TimeInterval (TTI) for transmissions and retransmissions and where thetiming relationship between transmissions and retransmissions ispre-determined, said radio base station comprising: a control circuitconfigured to transmit signaling via a base station transmitter, forconfiguring the mobile terminal to transmit information, according tothe second HARQ operation mode, relating to a first HARQ process using afirst predetermined number of transmission time intervals (TTIs)comprising at least a first TTI and a second TTI, to the radio basestation, wherein a redundancy version of the first HARQ process is sentin each TTI, and to retransmit the information, according to the secondHARQ operation mode, relating to the first HARQ process using a secondpredetermined number of TTIs, wherein the retransmission begins at leastat a second available retransmission occurrence according to the firstHARQ operation mode, subsequent to the first TTI; and a receiver forreceiving information relating to the first HARQ process using the firstpredetermined number of TTIs comprising at least the first TTI and thesecond TTI; wherein said control circuit is configured to transmit HARQfeedback, via the transmitter, in response to the received informationon the first determined number of TTIs.
 19. The radio base station ofclaim 18, wherein the retransmission is configured to begin at thesecond available retransmission occurrence according to the first HARQoperation mode, subsequent to the first TTI.
 20. The radio base stationof claim 18, wherein the control circuit is configured to transmitinformation indicating the first or second predetermined number of TTIs.21. The radio base station of claim 18, wherein the first predeterminednumber of TTI is equal to the second number of TTIs.
 22. The radio basestation of claim 18, wherein the control circuit is configured totransmit configuration information via Radio Resource Control (RRC)signaling that the first predetermined number of TTIs comprising atleast a first TTI and a second TTI should be used for all transmissions.